As a cooling structure of this kind, Japanese Patent Laid-Open Publication No. 2002-364456, for example, discloses a cylinder liner cooling structure which is provided with a sleeve including a plurality of small openings through which coolant flows in a water jacket. This cylinder liner cooling structure will be described with reference to FIG. 8.
As shown in FIG. 8, a sleeve 104 formed with a plurality of openings 103 is provided within a water jacket 101, or more specifically, between an outer wall and a cylinder liner 102 forming the water jacket 101, concentrically with the cylinder liner 102.
Coolant flows from an inlet 106 provided in a lower portion of the water jacket 101 through the openings 103 in the sleeve 104 within the water jacket 101 to an outlet 107 provided in an upper portion of the water jacket 101.
If the coolant inlet 106 is only provided at a single location, for example, the coolant does not flow well circumferentially of the water jacket 101, producing areas where the coolant is likely to stagnate. Consequently, high-temperature spots are produced locally in the cylinder liner 102, resulting in a nonuniform temperature distribution in the cylinder liner 102.
Also, the velocity of flow of the coolant passing through the openings 103 located far from the inlet 106 is smaller than that of the coolant passing through the openings 103 located near the inlet 106, due to the friction force acting on the coolant flow and reduction in the amount of flow by the amount flowing out through the openings 103 located near the inlet 106.
The differences in the flow velocity of the coolant passing through the openings 103 cause differences in the level of turbulence generated in the coolant passing through the openings 103 and striking the cylinder liner 102. In short, generation of turbulence is nonuniform by location within the water jacket 101. This causes heat transfer efficiency to be different by location, and thus causes a nonuniform temperature distribution in the cylinder liner 102 as above, preventing effective cooling of the cylinder liner 102.
Thus, there is a desire for an art which provides a more uniform temperature distribution in a cylinder liner to effectively cool the cylinder liner and increase cooling efficiency.
Japanese Utility Model Laid-Open Publication No. HEI-6-80821, for example, discloses another conventional cylinder liner cooling structure in which bores through which coolant fluid flows are formed in a cylinder liner, and a finned core is inserted into each bore. This cylinder liner cooling structure will be described with reference to FIGS. 9, 10A and 10B.
As shown in FIG. 9, a plurality of bores 202 are formed in a cylinder cover 201 of an internal combustion engine, and finned cores 203 are disposed in the respective bores 202. The clearance between the fins and the inner surface of the bore 202 is set at a predetermined dimension t (see FIG. 10A).
FIG. 10A is an enlarged view of the finned core 203 disposed in the bore 202.
As shown in FIG. 10B, when coolant fluid flows through the bore 202, turbulent flow in the coolant fluid occurs within the bore 202.
The cooling structure shown in FIG. 9 has the elongated bores 202 as passages for coolant fluid, and thus has difficulty in ensuring an adequate amount of flow of the coolant fluid as compared to a system of cooling a cylinder liner by a water jacket, for example, having a disadvantage in cooling capability. Also, since it can only cool portions near the bores 202, it is difficult to uniformly cool the entire cylinder liner by the bores 202 formed in the cylinder liner. If the number of the bores 202 is increased to increase the amount of flow of the coolant fluid, for example, the number of man-hours to form the bores 202 is increased, resulting in an increased manufacturing time.
In addition, since the finned core 203 consists of a shaft member and a large number of fins fixed on the shaft member, it is difficult to keep, in the elongated bore 202, the clearance between each fin and the inner surface of the bore 202 at the predetermined dimension, due to a bend of the shaft member and variations in the outside diameter of the fins. When the clearance exceeds the allowable range, there is no alternative to replacing the finned core 203 to adjust the clearance. There is thus a desire for a structure which allows precise formation of the clearance.
Furthermore, when a cylinder liner integrated with a cylinder block wears, for example, the cylinder liner cannot be replaced. If the cylinder block as a whole is made from cast iron to prevent wear of the cylinder liner, it leads to an increased weight of the cylinder block.
Thus, there is a desire for a cylinder liner cooling structure which allows more uniform cooling, easy manufacturing, and precise formation of a clearance between a distal edge of a fin and a wall opposite to the fin, and also allows replacement of a cylinder liner portion and a reduction in weight of a cylinder block.